Scientists may discover extraterrestrial life for the first time on the nearby moon

Saturn has 146 confirmed moons – more than any other planet in the solar system – but one, called Enceladus, stands out. It seems it contains the ingredients for life.

From 2004 to 2017, Cassini – a joint mission of NASA, the European Space Agency and the Italian Space Agency – explored Saturn, its rings and moons. Cassini drew impressive conclusions. Enceladus, with a diameter of only 504 kilometers, hides an ocean of liquid water beneath the icy crust that covers the entire moon.

Geysers at the moon’s south pole throw gas and ice grains formed from ocean water into space.

Although Cassini engineers did not intend to analyze the icicles actively emitted from Enceladus, they installed a dust analyzer on the spacecraft. This instrument measured the ejected icicles individually and told researchers about the composition of the subsurface ocean.

As a planetary scientist and astrobiologist who studies ice grains from Enceladus, I wonder if there is life on these or other icy moons. I also want to understand how scientists like me can detect it.

Ingredients for life

Like Earth’s oceans, Enceladus’ ocean contains salt, most of which is sodium chloride, known as table salt. The ocean also contains several carbon-based compounds and undergoes a process called tidal heating, which generates energy in the moon. Liquid water, carbon-based chemicals and energy are the most important ingredients of life.

In 2023, I and other scientists found phosphate, another essential compound, in ice grains from Enceladus’ ocean. Phosphate, a form of phosphorus, is essential for all life on Earth. It is part of DNA, cell membranes and bones. This was the first time scientists have found this compound in an alien water ocean.

The rocky core of Enceladus likely interacts with the watery ocean through hydrothermal vents. These hot, geyser-like structures protrude from the ocean floor. Scientists suggest that such an environment could be the birthplace of life on Earth.

Discovering potential life

To date, no one has discovered life beyond Earth. But scientists agree that Enceladus is a promising place to look for life. So how do we search?

In a paper published in March 2024, my colleagues and I conducted a laboratory test in which we simulated whether dust analysis instruments on spacecraft could detect and identify traces of life in ejected ice grains.

To simulate the detection of ice grains as recorded by dust analyzers in space, we used a laboratory setup on Earth. With this setup, we injected a small jet of water containing bacterial cells into a vacuum, where the jet broke up into droplets. Each drop theoretically contained one bacterial cell.

We then fired a laser at the individual droplets, creating charged ions from water and cell connections. We measured the charged ions using a method called mass spectrometry. These measurements helped us predict what the dust analysis instruments on the spacecraft would detect if they encountered a bacterial cell in an ice crumb.

We have found that these devices do a good job of identifying cell material. Instruments designed to analyze individual ice grains should be able to identify bacterial cells, even if an ice grain from an Enceladus-type geyser contains only 0.01 percent of the constituents of a single cell.

Analyzers can recognize a number of potential characteristics of cellular material, including amino acids and fatty acids. The amino acids detected are fragments of cell proteins or metabolites – small molecules involved in chemical reactions in the cell. Fatty acids are fragments of lipids that make up cell membranes.

In our experiments we used the bacterium Sphingopyxis alaskensis. The cells in this culture are extremely small – about the same size as the cells that would fit in the ice sheets ejected by Enceladus. In addition to their small size, these cells like cold environments and require only a few nutrients to survive and grow, just as life adapted to Enceladus’ ocean conditions would likely do.

The special dust analyzer on Cassina did not have the analytical capabilities to identify cell material in ice grains. However, scientists are already developing instruments with much greater capabilities for potential future Enceladus missions. Our experimental results will be used in the planning and development of these devices.

Future missions

Enceladus is one of the main targets for future missions by NASA and the European Space Agency. In 2022, NASA announced that the mission to Enceladus will be the second-highest priority when selecting the next major missions, with the mission to Uranus being the highest priority.

The European Space Agency recently announced that Enceladus is the main target of its next major mission. This mission will likely include a powerful dust analyzer to analyze ice grains.

Enceladus isn’t the only moon with an ocean of liquid water. Jupiter’s moon Europa also has an ocean that covers the entire moon under its icy crust. Ice grains on Europa float above its surface, and some scientists think Europa may even have Enceladus-like geysers blowing the grains into space. Our research will also help study ice grains from Europe.

NASA’s Europa Clipper mission will visit Europe in the coming years. Clipper is scheduled to launch in October 2024 and arrive at Jupiter in April 2030. One of the two mass spectrometers on the spacecraft, the SUrface Dust Analyzer, is designed to analyze individual ice grains.

The Surface Dust Analyzer on Clipper analyzes ice grains from Jupiter’s moon Europa. (NASA/CU Boulder/Glenn Asakawa)
Our study shows that this tool can find even small fractions of bacterial cells if they are present in just a few ejected ice grains.

Given the short-term plans of space agencies and the results of our research, the prospects for future space missions to Enceladus or Europa are incredibly exciting. We now know that scientists can use existing and future instruments to find out whether there is life on one of these moons.